Move symnode helpers to utils (#144158)
Summary:
X-link: https://github.com/pytorch/pytorch/pull/144158
Approved by: https://github.com/williamwen42, https://github.com/jansel
ghstack dependencies: #144129, #144130, #144141
Reviewed By: jeanschmidt
Differential Revision: D67828342
Pulled By: anijain2305
fbshipit-source-id: 6405bc99238af8d51a7ea59dc1ec785183466d36
